1. Field of the Invention
The present invention relates to a positive-working, radiation-sensitive recording material capable of being used for the production of planographic printing plates, and in particular, where the material comprises an aluminum support and a radiation-sensitive layer.
2. Description of Related Art
Radiation-sensitive recording materials for the production of planographic printing plates, such as presensitized printing plates or "PS-plates", are generally known. The layer weight of the radiation-sensitive layer in general is less than 3 g/m.sup.2. The recording material is usually brought into direct contact with the film original by evacuation, subjected to imagewise irradiation, preferably with UV-radiation, and subsequently developed. Aqueous-alkaline developers are customarily employed. The printing plate obtained in this way may be baked or gummed, or both, if appropriate.
A positive-working PS-plate is disclosed in JP-A 06-067 419 and DE-A 41 26 836. The PS-plate disclosed in these references comprises an aluminum support film which has been (i) electrolytically grained in hydrochloric acid, (ii) cleaned in sulfuric acid, (iii) anodized in sulfuric acid and (iv) rendered hydrophilic with polyvinylphosphonic acid. This support is coated with a radiation-sensitive layer which comprises a 1,2-naphthoquinone-2-diazide compound as the main radiation-sensitive component and a polymeric binder, e.g., a novolak. In order to be able to distinguish between irradiated and non-irradiated areas of the recording material, minor amounts of further radiation-sensitive components may be present, which on exposure generate or release a strong acid and, in a secondary reaction with a suitable dye, cause a color change in the radiation-sensitive layer. In order to reduce the evacuation time in the vacuum contact frame and to induce a uniform contact, the surface of the recording material may be roughened, e.g., by suitable particles. In the cited reference, these particles are silica particles which are partially embedded in the radiation-sensitive layer.
Continuous and discontinuous matting layers applied on top of the radiation-sensitive layer are also known from prior art.
To improve the developing process latitude, and to make the use of weakly alkaline developers possible, specific polymeric binders have been proposed. According to the teachings of JP-A 61-006 647 and DE-A 35 21 555, the binder may comprise at least two different novolak resins. They are obtained by co-polycondensation of 5 to 75 mole-% of phenol, 20 to 70 mole-% of m-cresol and/or o-cresol, and 5 to 75 mole-% of p-cresol with formaldehyde. In JP-A 61-205 933 and DE-A 36 07 598, a novolak resin is employed which has a weight average molecular weight M.sub.w of from 6,000 to 20,000 and a ratio of M.sub.w :M.sub.n (=polydispersity) of from 2 to 14.
JP-A 07-114 178 and EP-A 639 797 are directed to the problem of correcting film edge portions on lithographic printing plates. This problem particularly occurs when a positive working light-sensitive composition is provided on a support subjected to graining treatment and anodization treatment. Film edge corrections may also be required when a polymeric ortho-quinonediazide compound is employed. The problem may be solved by providing a light-sensitive composition which comprises a clathrate-forming, high-molecular weight compound. The high-molecular weight compound provides internal channels or other cavities into which low-molecular weight compounds fit. Preferred clathrate-forming compounds are cyclic D-glucanes, cyclophanes and, in particular, cyclodextrins.
Another problem is that generally, positive-working photosensitive lithographic printing plates are easily attacked by various processing chemicals used during printing, e.g., isopropyl alcohol contained in damping solutions. Consequently, printing plates which have been attacked by such processing chemicals will tend to have low print runs.
According to JP-A 01-302 349, 02-001 855, 02-029 750 and EP-A 345 016, this problem of sensitivity to processing chemicals may be solved by employing a photosensitive composition comprising 0.2 to 20% by weight of an activator compound in addition to the o-naphthoquinonediazide compound and the alkali-soluble resin. The activator is an ester or an ether of a polyoxyalkylene sorbitol fatty acid, an alkylene oxide adduct of castor oil, lanolin, lanolin alcohol, beeswax, phytosterol or phytostanol or it is an alkyl ether, alkylphenyl ether or alkyl ester of polyoxypropylene.
According to JP-A 63-223 637, 63-276 048, 63-303 343, 01-052 139 and EP-A 287 212, the resistance of printing plates to chemicals is also improved when specific high-molecular weight compounds are incorporated in the radiation-sensitive composition. The high-molecular weight compounds contain monomer units in which a hydroxy-substituted aromatic group, preferably a hydroxyphenyl group, is bound via an amide bond.
At present, there is no PS-plate available which overcomes all the disadvantages discussed above.